Air freight cold chain comes in two forms. Passive packaging holds temperature with insulation and a thermal mass. Active packaging runs a refrigeration unit. They cost very different amounts and fail in very different ways.
Passive
An insulated shipper, from a small parcel box to a full pallet unit, loaded with a refrigerant: gel packs, phase change material conditioned to a specific temperature, or dry ice for frozen and ultra-cold.
- Duration: typically 48 to 120 hours, with high performance vacuum insulated panel systems reaching 96 to 168 hours.
- No power, no monitoring, no intervention. Once it is closed it either works or it does not.
- Cheaper per shipment, widely available, and it can go on any aircraft to any airport.
- Highly sensitive to conditioning and packout. A phase change material conditioned to the wrong temperature, or a box packed with the wrong number of panels, fails silently.
Passive is right for smaller volumes, shorter lanes, and any route where ground handling is unreliable, precisely because it needs nothing from anyone.
Active
A powered, insulated ULD-sized container with its own compressor or dry ice based cooling, running off a battery and rechargeable at stations. The market names most people encounter are Envirotainer, CSafe and DoKaSch.
- Duration: effectively as long as the power lasts and can be recharged, so several days and upward, and it recovers after a door opening.
- Tighter control, often to within a degree, with an actual setpoint rather than a decay curve.
- Requires the airline and ground handler to support it: charging, correct handling and a station that stocks the units.
- Much more expensive per shipment, and hire is charged per day including repositioning.
Active is right for high value pharmaceutical loads, long or multi-leg routings, and anything where a single failure costs more than the whole year's container hire.
Dry ice makes it a dangerous goods shipment
Dry ice is UN 1845, Class 9. Using it as a refrigerant brings dangerous goods obligations even when the product itself is not regulated:
- The package must carry the Class 9 label and UN 1845 with the net quantity of dry ice in kilograms.
- The air waybill must show the number of packages and the total dry ice weight.
- It must appear on the NOTOC, the notification to captain, so the crew know what is aboard.
- Aircraft have limits on total dry ice, because it sublimates to carbon dioxide and displaces oxygen. This is a real capacity constraint on lanes carrying a lot of frozen pharma, and it is why a booking can be refused for a reason unrelated to space or weight.
Dry ice sublimates at roughly 1 to 2 percent of mass per hour depending on the packaging, so the pack-out has to be sized for the worst case transit time, including delays, not the scheduled one. See the nine dangerous goods classes.
Choosing between them
- Map the worst case transit time, door to door, including a missed connection and a weekend. Not the schedule.
- Compare that against the qualified duration of the passive solution, with margin. If the two are close, go active or go to a higher performance passive system.
- Check station capability at every touchpoint for active units, and at transit points for dry ice replenishment.
- Price the failure, not the packaging. A container hire that looks expensive is trivial against one rejected batch.
- Qualify the lane for whichever you choose, per GDP requirements, and monitor it per data loggers and excursions.
General guidance. Qualified duration, conditioning procedures and dry ice limits are specific to the packaging system, the airline and the route.
